This is what the connector on the wiring harness looks like. You can see pin 2 is labeled "rev." Here's the adapter that comes with the head unit. The white plug with three black wires plugs into the wiring harness. The three black wires are the steering wheel controls (labeled SWG, SW2, SW1). You just need to make sure that the backup signal wire (the single black/orange) goes into pin 2. The harness connector above is for 2013 and before. I had to hack that connector to make it work with my 2014.
Yes, I still have it. I don't know if this unit can be used with JBL. The safe answer is "probably not", but I don't know well enough to say for sure.